1. Field of the Invention
The present invention relates to a local etching apparatus and a local etching method for locally etching a protrusion on a surface of a wafer by radicals or locally etching a relatively thick portion of a wafer so as to make the distribution of thickness of the wafer uniform.
2. Description of the Related Art
FIG. 10 is a schematic sectional view of an example of a local etching apparatus of the related art.
This local etching apparatus is provided with a discharge tube 100, a gas feed device 110, a plasma generator 120, and a stage 130.
Due to this configuration, it is possible to feed gas from the gas feed device 110 to the discharge tube 100, generate microwaves M from a microwave generator 121 of the plasma generator 120 to the inside of a waveguide 122 to cause plasma discharge of the gas in the discharge tube 100, and spray the radicals G produced by the plasma discharge from a nozzle portion 101 of the discharge tube 100 on to a wafer W on the stage 130.
By making the stage 130 move in the horizontal direction, a portion Wa relatively thicker than a defined thickness on the surface of the wafer W (hereinafter referred to as a "relatively thick portion") is guided directly under the nozzle 101 where the radicals G are sprayed from the nozzle 101 to the relatively thick portion Wa to locally etch the relatively thick portion Wa. By locally etching the entire surface of the wafer W in this way, it is possible to make the distribution of the surface thickness of the wafer W uniform and flatten the surface of the wafer W as a whole.
The above local etching apparatus of the related art, however, had the following problems.
The depth of local etching of the wafer W by the radicals G depends on the temperature of the discharge tube 100.
FIG. 11 is a graph depicting the correlation between the surface temperature of the discharge tube 100 and the etching depth.
As shown in FIG. 11, the etching depth by the radicals G increases with the rise of the surface temperature of the discharge tube 100. When the surface temperature of the discharge tube 100 reaches a certain value T.sub.0, the etching depth at temperatures above the temperature T.sub.0 becomes substantially constant.
At the time of ignition of the plasma discharge in the discharge tube 100, the discharge tube 100 is cold. The temperature of the discharge tube 100 rises in time due to the heat of the plasma. Therefore, the etching depth of the wafer W by the radicals G will not stabilize until the surface temperature of the discharge tube 100 reaches temperature T.sub.0. Accordingly, if the etching work is commenced before the surface temperature of the discharge tube 100 reaches T.sub.0, the etching rate of the wafer W becomes unstable and it is not possible to flatten the wafer W to a high precision. In view of this, in the local etching apparatuses of the related art, it was necessary to allow for a long standby time for the surface temperature of the discharge tube 100 to reach T.sub.0. It was not possible to start the etching work during the standby period. As a result, the throughput of the flattening of the wafer W was low and the mass producibility was poor.